LV belongs to the Picornavirus family and is therefore an RNA virus. LV was first identified in bank voles (Clethrionomys glareolus) and is known to cause disease in a number of animals. Three isolates of the virus (87-012, 174F and 145SL) were disclosed in International Patent Application WO 98/11133 and the partial sequence of each isolate disclosed therein. The full sequences of the three LV's were subsequently published (Johansson et al., J. Virol., 76, 8920-8930, 2002).
Comparative sequence analysis of the LV prototype strain, 87-012, and two other serologically related LV isolates, 174F and 145SL, revealed that the genomes of these newly determined Swedish LV strains are closely related and possess the following deviant picornavirus-like organization (Johansson et al., 2002, supra):
5′UTR-VP0-VP3-VP1-2A1-2A2-2B-2C-3A-3B-3C-3D-3′UTR.
Phylogenetic analysis showed that the LV isolates constitute a distinct monophyletic group, which, together with the genus Parechovirus, is separated from other members of the Picornaviridae (Johansson et al., 2002, supra; Lindberg and Johansson, Virus Res., 85, 61-70, 2002). Furthermore, a complete genomic sequence of another virus, M1146, which was isolated from another vole species (Microtus montanus), trapped in Oregon, USA, verified that this virus is also a member of the Picornaviridae, most closely related to the LVs isolated in Sweden and is a new genotype within the distinct LV cluster (Johansson et al., J. Gen. Virol., 84, 837-844, 2003).
LV has been found in humans and can cause a variety of diseases. The identification of LV in Swedish and North American voles suggests a continuous presence of LV over a wide geographical range throughout numerous vole populations. Presently, there exist seven known strains of LV, namely 87-012 (NC 003976; AF327920), 174F (AF327921), 145SL (AF327922) and 342SL (B. Niklasson, unpublished data) originated from Sweden, and M1146 (AF538689), NY64-7855 (unpublished data) and NY64-7947 (unpublished data) originated from the USA. NCBI Genbank accession numbers or other sources are shown in brackets.
Genetically the LV genome and the encoded polyproteins exhibit several exceptional features, such as the absence of a predicted maturation cleavage of VP0, a conserved sequence determinant in VP0 that is typically found in VP1 of other Picornaviruses, and a cluster of two unrelated 2A proteins, namely 2A1 and 2A2 (Johansson et al., 2002, supra). The 2A1 protein is related to the 2A protein of cardio-, erbo-, tescho- and aphthoviruses and the 2A2 protein is related to the 2A protein of parechoviruses, kobuviruses and avian encephalomyelitis virus (Johansson et al., 2002, supra; Lindberg and Johansson, Virus Research, 85, 61-70, 2002).
LV is characterised by a chronic or long lasting infection in its rodent host and reservoir. LV infects different species of animals as well as humans and the infection may result in a long lasting or chronic infection. LV replicates in a wide variety of tissue culture cells giving a chronic infection with discrete cytopathogenic effect (CPE) and low viral output (in the order of 1000-100 000 viral particles per ml supernatant).
Data generated by virus cultivation under laboratory conditions show that LV grows/replicates in a number of cell lines that originate from different tissues and different species, e.g. Vero monkey kidney; Vero E6 monkey kidney; MA-104 monkey kidney; CV-1 monkey kidney; GMK monkey kidney; A-549 human lung; Hela human cervical tissue; BHK 21 hamster kidney; RD human muscle; and L-cells mouse skin.
In animals and humans, LV replicates in muscle tissue, including heart tissue, in neural cell, including the brain, and in endocrine glands, including the beta cells of the pancreas, the thyroid gland and the supra renal gland.
Data generated by detection of virus using LV specific immunohistochemistry tests and thin section electron microscopy in humans, bank voles, lemmings, laboratory mice rabbits, guinea pigs, arctic foxes and moose show that LV has been found in endocrine and exocrine pancreas tissue, in endothelial cells of vessels, cells in the brain (including nerve tissue), cells of the liver, cells of the placenta and the umbilical cord, muscle tissue, heart tissue and tissue of the thyroid gland (Niklasson et al., Ann NY Acad Sci, 1005, 170-175, 2003; and unpublished data).
It can therefore be concluded that LV can grow in most cell types of the body and therefore infect all organs of the body.
The most closely related animal viruses to LV are viruses in the cardiovirus genus.
Similarities
Cardioviruses belong to the picornavirus family.
Cardiovirus have rodents as their natural reservoir.
Cardioviruses can cause disease in a wide variety of animal species.
Cardiovirus can infect and cause disease in the same organs as LV.
Differences
Cardiovirus and LV are genetically distantly related.
The double 2 A of LV is absent in cardiovirus.
Cardiovirus is not related to LV by serology.
Cardiovirus cause an acute disease (not long lasting or chronic) when it affects its non-rodent victims.
Cardiovirus is easy to cultivate in tissue culture without adaptation while LV is often impossible to cultivate without blind passage in tissue culture or first passage in suckling mice and after several passages in suckling mice adaptation in tissue culture (see Johansson et al., BBRC, 317, 1023-1029, 2004).
Cardioviruses generally do not infect humans (only rare case reports in the literature e.g., Zimmerman, Encephalomyocarditis, In Handbook: Series of Zoonoses, G. B. Beran (Ed.), CRC Press Inc., Boca Raton, Fla., USA, 1994; and Tesh, Am. J. Trop. Med. Hyg., 27, 144-149, 1978).
It is likely that new variants of LV in different continents will be identified. As LVs are associated with a number of disease conditions it is desirable to have a simple efficient and effective test for detecting LVs. The test will need to be specific so that only LVs are detected and not other picornaviruses. Furthermore, it is desirable that the test can be used to detect all LVs strains, is highly specific and highly sensitive. It is also desirable that the test allows the quantitative measurement of LV so that the viral load can be determined.
In International Patent Application WO 2004/073710, the use of an antiviral agent to treat disease caused by LV infections is disclosed. By being able to test for the presence of LV the effectiveness of such treatments can be monitored, especially if the test is quantitative.
The current tests for the presence of LV are either very laborious, e.g., virus culture/isolation and detection of CPE, or not sensitive enough, e.g., immunohistochemistry tests, which do not detect all LVs or do not distinguish effectively between LVs and other picornaviruses.
There is therefore a need for a simple effective test for specifically detecting LV.